It is known that, in a known manner, a twin-flow turbojet comprises:                a hot-flow generator (also known as the main flow) which extends along a longitudinal axis and which is coupled by means of a front attachment and a rear attachment to a suspension mast belonging to the structure of an aircraft. The hot-flow generator is delimited by an annular cowl which forms the casing of the latter and which terminates downstream in a nozzle for discharging the main flow;        a cold-flow fan of which the rotation axis is indistinguishable from the longitudinal axis of the hot-flow generator which rotates the latter; and        a nacelle which surrounds the hot-flow generator and the cold-flow fan and which delimits an external channel of cold flow, that is asymmetrical relative to the longitudinal axis of the hot-flow generator and has an annular section around the latter. The cold flow, compressed by the fan, is thus guided toward the outside by the cold-flow channel.        
It is also known that, in the case of a separated twin-flow turbojet, the main and bypass flows are discharged separately in two concentric flows. For this reason the nacelle comprises a casing surrounding the fan part which terminates downstream in a nozzle for discharging the bypass flow.
Furthermore, a ventilation flow travels along the hot-flow generator to cool it. In order to minimize performance losses, this ventilation flow must be discharged to the outside of the turbojet at a pressure close to the ambient pressure. For this, it is known practice to arrange a slot of circular shape in the cowl of the main nozzle of the turbojet through which the ventilation flow can escape. In particular, this slot extends on either side of the suspension mast of the turbojet and is delimited by two circular contours of different diameter: the diameter of the contour of the upstream portion of the cowl of the main nozzle being greater than that of the downstream portion of said cowl. In this manner, the ventilation flow escapes through the slot and then runs along the outer face of the downstream portion of the cowl of the main nozzle and is thus mixed with the bypass flow.
Moreover, and for reasons of fire safety, the certification authorities require the slot to be closed off on each lateral side of the mast over a determined angular sector (for example equal to 45°).
However, the closing-off of the slot—by means of a partition connecting, along the two predefined angular sectors, the upstream and downstream portions of the cowl of the main nozzle—results in the formation of a dog leg (or “step down”) which disrupts the bypass flow on the main nozzle causing a recirculation of said flow. This leads to aerodynamic losses adversely affecting the performance of the turbojet.
To alleviate this drawback, an additional convex curved fairing is provided, in a known manner, to cover the dog leg formed by the partial closing-off of the slot. Such a fairing extends from said slot to the trailing edge of the main nozzle.
However, this curved fairing causes a great acceleration of the bypass flow and a risk of interaction with the canopy system supporting the turbojet, these factors being capable of causing undesirable aerodynamic losses.